/**
 * @file
 * Address Resolution Protocol module for IP over Ethernet
 *
 * Functionally, ARP is divided into two parts. The first maps an IP address
 * to a physical address when sending a packet, and the second part answers
 * requests from other machines for our physical address.
 *
 * This implementation complies with RFC 826 (Ethernet ARP). It supports
 * Gratuitious ARP from RFC3220 (IP Mobility Support for IPv4) section 4.6
 * if an interface calls etharp_query(our_netif, its_ip_addr, NULL) upon
 * address change.
 */

/*
 * Copyright (c) 2001-2003 Swedish Institute of Computer Science.
 * Copyright (c) 2003-2004 Leon Woestenberg <leon.woestenberg@axon.tv>
 * Copyright (c) 2003-2004 Axon Digital Design B.V., The Netherlands.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 *
 */

#include "lwip/opt.h"
#include "lwip/inet.h"
#include "netif/etharp.h"
#include "lwip/ip.h"
#include "lwip/stats.h"

/* ARP needs to inform DHCP of any ARP replies? */
#if (LWIP_DHCP && DHCP_DOES_ARP_CHECK)
#  include "lwip/dhcp.h"
#endif

/** the time an ARP entry stays valid after its last update,
 * (240 * 5) seconds = 20 minutes.
 */
#define ARP_MAXAGE 240
/** the time an ARP entry stays pending after first request,
 * (2 * 5) seconds = 10 seconds.
 *
 * @internal Keep this number at least 2, otherwise it might
 * run out instantly if the timeout occurs directly after a request.
 */
#define ARP_MAXPENDING 2

#define HWTYPE_ETHERNET 1

/** ARP message types */
#define ARP_REQUEST 1
#define ARP_REPLY 2

#define ARPH_HWLEN(hdr) (ntohs((hdr)->_hwlen_protolen) >> 8)
#define ARPH_PROTOLEN(hdr) (ntohs((hdr)->_hwlen_protolen) & 0xff)

#define ARPH_HWLEN_SET(hdr, len) (hdr)->_hwlen_protolen = htons(ARPH_PROTOLEN(hdr) | ((len) << 8))
#define ARPH_PROTOLEN_SET(hdr, len) (hdr)->_hwlen_protolen = htons((len) | (ARPH_HWLEN(hdr) << 8))

enum etharp_state {
        ETHARP_STATE_EMPTY,
        ETHARP_STATE_PENDING,
        ETHARP_STATE_STABLE,
        /** @internal transitional state used in etharp_tmr() for convenience*/
        ETHARP_STATE_EXPIRED
};

struct etharp_entry
{
#if ARP_QUEUEING
        /**
         * Pointer to queue of pending outgoing packets on this ARP entry.
         */
        struct pbuf *p;
#endif
        struct ip_addr ipaddr;
        struct eth_addr ethaddr;
        enum etharp_state state;
        u8_t ctime;
};

static const struct eth_addr ethbroadcast =
        {
                {
                        0xff,0xff,0xff,0xff,0xff,0xff
                }
        };
static struct etharp_entry arp_table[ARP_TABLE_SIZE];

/**
 * Try hard to create a new entry - we want the IP address to appear in
 * the cache (even if this means removing an active entry or so). */
#define ETHARP_TRY_HARD 1

static s8_t find_entry(struct ip_addr *ipaddr, u8_t flags);
static err_t update_arp_entry(struct netif *netif, struct ip_addr *ipaddr, struct eth_addr *ethaddr, u8_t flags);
/**
 * Initializes ARP module.
 */
void etharp_init(void)
{
        u8_t i;
        /* clear ARP entries */
        for (i = 0; i < ARP_TABLE_SIZE; ++i) {
                arp_table[i].state = ETHARP_STATE_EMPTY;
#if ARP_QUEUEING
                arp_table[i].p = NULL;
#endif
                arp_table[i].ctime = 0;
        }
}

/**
 * Clears expired entries in the ARP table.
 *
 * This function should be called every ETHARP_TMR_INTERVAL microseconds (5 seconds),
 * in order to expire entries in the ARP table.
 */
void etharp_tmr(void)
{
        u8_t i;

        LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer\n"));
        /* remove expired entries from the ARP table */
        for (i = 0; i < ARP_TABLE_SIZE; ++i) {
                arp_table[i].ctime++;
                /* stable entry? */
                if ((arp_table[i].state == ETHARP_STATE_STABLE) &&
                                /* entry has become old? */
                                (arp_table[i].ctime >= ARP_MAXAGE)) {
                        LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer: expired stable entry %"U16_F".\n", (u16_t)i));
                        arp_table[i].state = ETHARP_STATE_EXPIRED;
                        /* pending entry? */
                } else if (arp_table[i].state == ETHARP_STATE_PENDING) {
                        /* entry unresolved/pending for too long? */
                        if (arp_table[i].ctime >= ARP_MAXPENDING) {
                                LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer: expired pending entry %"U16_F".\n", (u16_t)i));
                                arp_table[i].state = ETHARP_STATE_EXPIRED;
#if ARP_QUEUEING
                        } else if (arp_table[i].p != NULL) {
                                /* resend an ARP query here */
                                //FIXME: netif not recored in ARP table, use first in list instead
                                if(netif_list != NULL)
                                        etharp_request(netif_list, &arp_table[i].ipaddr);
#endif
                        }
                }
                /* clean up entries that have just been expired */
                if (arp_table[i].state == ETHARP_STATE_EXPIRED) {
#if ARP_QUEUEING
                        /* and empty packet queue */
                        if (arp_table[i].p != NULL) {
                                /* remove all queued packets */
                                LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer: freeing entry %"U16_F", packet queue %x.\n", (u16_t)i, (void *)(arp_table[i].p)));
                                pbuf_free(arp_table[i].p);
                                arp_table[i].p = NULL;
                        }
#endif
                        /* recycle entry for re-use */
                        arp_table[i].state = ETHARP_STATE_EMPTY;
                }
        }
}

/**
 * Search the ARP table for a matching or new entry.
 *
 * If an IP address is given, return a pending or stable ARP entry that matches
 * the address. If no match is found, create a new entry with this address set,
 * but in state ETHARP_EMPTY. The caller must check and possibly change the
 * state of the returned entry.
 *
 * If ipaddr is NULL, return a initialized new entry in state ETHARP_EMPTY.
 *
 * In all cases, attempt to create new entries from an empty entry. If no
 * empty entries are available and ETHARP_TRY_HARD flag is set, recycle
 * old entries. Heuristic choose the least important entry for recycling.
 *
 * @param ipaddr IP address to find in ARP cache, or to add if not found.
 * @param flags
 * - ETHARP_TRY_HARD: Try hard to create a entry by allowing recycling of
 * active (stable or pending) entries.
 *
 * @return The ARP entry index that matched or is created, ERR_MEM if no
 * entry is found or could be recycled.
 */
static s8_t find_entry(struct ip_addr *ipaddr, u8_t flags)
{
        s8_t old_pending = ARP_TABLE_SIZE, old_stable = ARP_TABLE_SIZE;
        s8_t empty = ARP_TABLE_SIZE;
        u8_t i = 0, age_pending = 0, age_stable = 0;
#if ARP_QUEUEING
        /* oldest entry with packets on queue */
        s8_t old_queue = ARP_TABLE_SIZE;
        /* its age */
        u8_t age_queue = 0;
#endif

        /**
         * a) do a search through the cache, remember candidates
         * b) select candidate entry
         * c) create new entry
         */

        /* a) in a single search sweep, do all of this
         * 1) remember the first empty entry (if any)
         * 2) remember the oldest stable entry (if any)
         * 3) remember the oldest pending entry without queued packets (if any)
         * 4) remember the oldest pending entry with queued packets (if any)
         * 5) search for a matching IP entry, either pending or stable
         *    until 5 matches, or all entries are searched for.
         */

        for (i = 0; i < ARP_TABLE_SIZE; ++i)
        {
                /* no empty entry found yet and now we do find one? */
                if ((empty == ARP_TABLE_SIZE) && (arp_table[i].state == ETHARP_STATE_EMPTY)) {
                        LWIP_DEBUGF(ETHARP_DEBUG, ("find_entry: found empty entry %"U16_F"\n", (u16_t)i));
                        /* remember first empty entry */
                        empty = i;
                }
                /* pending entry? */
                else if (arp_table[i].state == ETHARP_STATE_PENDING) {
                        /* if given, does IP address match IP address in ARP entry? */
                        if (ipaddr && ip_addr_cmp(ipaddr, &arp_table[i].ipaddr)) {
                                LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("find_entry: found matching pending entry %"U16_F"\n", (u16_t)i));
                                /* found exact IP address match, simply bail out */
                                return i;
#if ARP_QUEUEING
                                /* pending with queued packets? */
                        } else if (arp_table[i].p != NULL) {
                                if (arp_table[i].ctime >= age_queue) {
                                        old_queue = i;
                                        age_queue = arp_table[i].ctime;
                                }
#endif
                                /* pending without queued packets? */
                        } else {
                                if (arp_table[i].ctime >= age_pending) {
                                        old_pending = i;
                                        age_pending = arp_table[i].ctime;
                                }
                        }
                }
                /* stable entry? */
                else if (arp_table[i].state == ETHARP_STATE_STABLE) {
                        /* if given, does IP address match IP address in ARP entry? */
                        if (ipaddr && ip_addr_cmp(ipaddr, &arp_table[i].ipaddr)) {
                                LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("find_entry: found matching stable entry %"U16_F"\n", (u16_t)i));
                                /* found exact IP address match, simply bail out */
                                return i;
                                /* remember entry with oldest stable entry in oldest, its age in maxtime */
                        } else if (arp_table[i].ctime >= age_stable) {
                                old_stable = i;
                                age_stable = arp_table[i].ctime;
                        }
                }
        }
        /* { we have no match } => try to create a new entry */

        /* no empty entry found and not allowed to recycle? */
        if ((empty == ARP_TABLE_SIZE) && ((flags & ETHARP_TRY_HARD) == 0))
        {
                return (s8_t)ERR_MEM;
        }

        /* b) choose the least destructive entry to recycle:
         * 1) empty entry
         * 2) oldest stable entry
         * 3) oldest pending entry without queued packets
         * 4) oldest pending entry without queued packets
         * 
         * { ETHARP_TRY_HARD is set at this point }
         */

        /* 1) empty entry available? */
        if (empty < ARP_TABLE_SIZE)
        {
                i = empty;
                LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("find_entry: selecting empty entry %"U16_F"\n", (u16_t)i));
        }
        /* 2) found recyclable stable entry? */
        else if (old_stable < ARP_TABLE_SIZE)
        {
                /* recycle oldest stable*/
                i = old_stable;
                LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("find_entry: selecting oldest stable entry %"U16_F"\n", (u16_t)i));
#if ARP_QUEUEING
                /* no queued packets should exist on stable entries */
                LWIP_ASSERT("arp_table[i].p == NULL", arp_table[i].p == NULL);
#endif
                /* 3) found recyclable pending entry without queued packets? */
        } else if (old_pending < ARP_TABLE_SIZE)
        {
                /* recycle oldest pending */
                i = old_pending;
                LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("find_entry: selecting oldest pending entry %"U16_F" (without queue)\n", (u16_t)i));
#if ARP_QUEUEING
                /* 4) found recyclable pending entry with queued packets? */
        } else if (old_queue < ARP_TABLE_SIZE)
        {
                /* recycle oldest pending */
                i = old_queue;
                LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("find_entry: selecting oldest pending entry %"U16_F", freeing packet queue %p\n", (u16_t)i, (void *)(arp_table[i].p)));
                pbuf_free(arp_table[i].p);
                arp_table[i].p = NULL;
#endif
                /* no empty or recyclable entries found */
        } else
        {
                return (s8_t)ERR_MEM;
        }

        /* { empty or recyclable entry found } */
        LWIP_ASSERT("i < ARP_TABLE_SIZE", i < ARP_TABLE_SIZE);

        /* recycle entry (no-op for an already empty entry) */
        arp_table[i].state = ETHARP_STATE_EMPTY;

        /* IP address given? */
        if (ipaddr != NULL)
        {
                /* set IP address */
                ip_addr_set(&arp_table[i].ipaddr, ipaddr);
        }
        arp_table[i].ctime = 0;
        return (err_t)i;
}

/**
 * Update (or insert) a IP/MAC address pair in the ARP cache.
 *
 * If a pending entry is resolved, any queued packets will be sent
 * at this point.
 *
 * @param ipaddr IP address of the inserted ARP entry.
 * @param ethaddr Ethernet address of the inserted ARP entry.
 * @param flags Defines behaviour:
 * - ETHARP_TRY_HARD Allows ARP to insert this as a new item. If not specified,
 * only existing ARP entries will be updated.
 *
 * @return
 * - ERR_OK Succesfully updated ARP cache.
 * - ERR_MEM If we could not add a new ARP entry when ETHARP_TRY_HARD was set.
 * - ERR_ARG Non-unicast address given, those will not appear in ARP cache.
 *
 * @see pbuf_free()
 */
static err_t update_arp_entry(struct netif *netif, struct ip_addr *ipaddr, struct eth_addr *ethaddr, u8_t flags)
{
        s8_t i, k;
        LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE | 3, ("update_arp_entry()\n"));
        LWIP_ASSERT("netif->hwaddr_len != 0", netif->hwaddr_len != 0);
        LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("update_arp_entry: %"U16_F".%"U16_F".%"U16_F".%"U16_F" - %02"X16_F":%02"X16_F":%02"X16_F":%02"X16_F":%02"X16_F":%02"X16_F"\n",
                                               ip4_addr1(ipaddr), ip4_addr2(ipaddr), ip4_addr3(ipaddr), ip4_addr4(ipaddr),
                                               ethaddr->addr[0], ethaddr->addr[1], ethaddr->addr[2],
                                               ethaddr->addr[3], ethaddr->addr[4], ethaddr->addr[5]));
        /* non-unicast address? */
        if (ip_addr_isany(ipaddr) ||
                        ip_addr_isbroadcast(ipaddr, netif) ||
                        ip_addr_ismulticast(ipaddr))
        {
                LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("update_arp_entry: will not add non-unicast IP address to ARP cache\n"));
                return ERR_ARG;
        }
        /* find or create ARP entry */
        i = find_entry(ipaddr, flags);
        /* bail out if no entry could be found */
        if (i < 0) return (err_t)i;

        /* mark it stable */
        arp_table[i].state = ETHARP_STATE_STABLE;

        LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("update_arp_entry: updating stable entry %"S16_F"\n", (s16_t)i));
        /* update address */
        for (k = 0; k < netif->hwaddr_len; ++k)
        {
                arp_table[i].ethaddr.addr[k] = ethaddr->addr[k];
        }
        /* reset time stamp */
        arp_table[i].ctime = 0;
        /* this is where we will send out queued packets! */
#if ARP_QUEUEING
        while (arp_table[i].p != NULL)
        {

                /* get the first packet on the queue */
                struct pbuf *p = arp_table[i].p;
                /* Ethernet header */
                struct eth_hdr *ethhdr = p->payload;
                /* remember (and reference) remainder of queue */
                /* note: this will also terminate the p pbuf chain */
               // sysprintf("send arp Q packet\n");
                arp_table[i].p = pbuf_dequeue(p);
                /* fill-in Ethernet header */
                for (k = 0; k < netif->hwaddr_len; ++k) {
                        ethhdr->dest.addr[k] = ethaddr->addr[k];
                        ethhdr->src.addr[k] = netif->hwaddr[k];
                }
                ethhdr->type = htons(ETHTYPE_IP);
                LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("update_arp_entry: sending queued IP packet %p.\n", (void *)p));
                /* send the queued IP packet */
                netif->linkoutput(netif, p);
                /* free the queued IP packet */
                pbuf_free(p);
        }
#endif
        return ERR_OK;
}

/**
 * Updates the ARP table using the given IP packet.
 *
 * Uses the incoming IP packet's source address to update the
 * ARP cache for the local network. The function does not alter
 * or free the packet. This function must be called before the
 * packet p is passed to the IP layer.
 *
 * @param netif The lwIP network interface on which the IP packet pbuf arrived.
 * @param pbuf The IP packet that arrived on netif.
 *
 * @return NULL
 *
 * @see pbuf_free()
 */
void etharp_ip_input(struct netif *netif, struct pbuf *p)
{
        struct ethip_hdr *hdr;
        LWIP_ASSERT("netif != NULL", netif != NULL);
        /* Only insert an entry if the source IP address of the
           incoming IP packet comes from a host on the local network. */
        hdr = p->payload;
        /* source is not on the local network? */
        if (!ip_addr_netcmp(&(hdr->ip.src), &(netif->ip_addr), &(netif->netmask)))
        {
                /* do nothing */
                return;
        }

        LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_ip_input: updating ETHARP table.\n"));
        /* update ARP table */
        /* @todo We could use ETHARP_TRY_HARD if we think we are going to talk
         * back soon (for example, if the destination IP address is ours. */
        update_arp_entry(netif, &(hdr->ip.src), &(hdr->eth.src), 0);
}


/**
 * Responds to ARP requests to us. Upon ARP replies to us, add entry to cache
 * send out queued IP packets. Updates cache with snooped address pairs.
 *
 * Should be called for incoming ARP packets. The pbuf in the argument
 * is freed by this function.
 *
 * @param netif The lwIP network interface on which the ARP packet pbuf arrived.
 * @param pbuf The ARP packet that arrived on netif. Is freed by this function.
 * @param ethaddr Ethernet address of netif.
 *
 * @return NULL
 *
 * @see pbuf_free()
 */
void etharp_arp_input(struct netif *netif, struct eth_addr *ethaddr, struct pbuf *p)
{
        struct etharp_hdr *hdr;
        /* these are aligned properly, whereas the ARP header fields might not be */
        struct ip_addr sipaddr, dipaddr;
        u8_t i;
        u8_t for_us;

        LWIP_ASSERT("netif != NULL", netif != NULL);

        

        /* drop short ARP packets */
        if (p->tot_len < sizeof(struct etharp_hdr))
        {
                LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE | 1, ("etharp_arp_input: packet dropped, too short (%"S16_F"/%"S16_F")\n", p->tot_len, sizeof(struct etharp_hdr)));
                pbuf_free(p);
                return;
        }

        hdr = p->payload;

        /* get aligned copies of addresses */
        *(struct ip_addr2 *)&sipaddr = hdr->sipaddr;
        *(struct ip_addr2 *)&dipaddr = hdr->dipaddr;

        /* this interface is not configured? */
        if (netif->ip_addr.addr == 0)
        {
                for_us = 0;
        } else
        {
                /* ARP packet directed to us? */
                for_us = ip_addr_cmp(&dipaddr, &(netif->ip_addr));
        }

        /* ARP message directed to us? */
        if (for_us)
        {

                /* add IP address in ARP cache; assume requester wants to talk to us.
                 * can result in directly sending the queued packets for this host. */
                update_arp_entry(netif, &sipaddr, &(hdr->shwaddr), ETHARP_TRY_HARD);
                /* ARP message not directed to us? */
        } else
        {
                /* update the source IP address in the cache, if present */
                update_arp_entry(netif, &sipaddr, &(hdr->shwaddr), 0);
        }

        /* now act on the message itself */
        switch (htons(hdr->opcode))
        {
                /* ARP request? */
        case ARP_REQUEST:
                /* ARP request. If it asked for our address, we send out a
                 * reply. In any case, we time-stamp any existing ARP entry,
                 * and possiby send out an IP packet that was queued on it. */

                LWIP_DEBUGF (ETHARP_DEBUG | DBG_TRACE, ("etharp_arp_input: incoming ARP request\n"));
                /* ARP request for our address? */
                if (for_us) {

                        LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_arp_input: replying to ARP request for our IP address\n"));
                        /* re-use pbuf to send ARP reply */
                        hdr->opcode = htons(ARP_REPLY);

                        hdr->dipaddr = hdr->sipaddr;
                        hdr->sipaddr = *(struct ip_addr2 *)&netif->ip_addr;

                        for (i = 0; i < netif->hwaddr_len; ++i) {
                                hdr->dhwaddr.addr[i] = hdr->shwaddr.addr[i];
                                hdr->shwaddr.addr[i] = ethaddr->addr[i];
                                hdr->ethhdr.dest.addr[i] = hdr->dhwaddr.addr[i];
                                hdr->ethhdr.src.addr[i] = ethaddr->addr[i];
                        }

                        hdr->hwtype = htons(HWTYPE_ETHERNET);
                        ARPH_HWLEN_SET(hdr, netif->hwaddr_len);

                        hdr->proto = htons(ETHTYPE_IP);
                        ARPH_PROTOLEN_SET(hdr, sizeof(struct ip_addr));

                        hdr->ethhdr.type = htons(ETHTYPE_ARP);
                        /* return ARP reply */
                        netif->linkoutput(netif, p);
                        /* we are not configured? */
                } else if (netif->ip_addr.addr == 0) {
                        /* { for_us == 0 and netif->ip_addr.addr == 0 } */
                        LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_arp_input: we are unconfigured, ARP request ignored.\n"));
                        /* request was not directed to us */
                } else {
                        /* { for_us == 0 and netif->ip_addr.addr != 0 } */
                        LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_arp_input: ARP request was not for us.\n"));
                }
                break;
        case ARP_REPLY:
                /* ARP reply. We already updated the ARP cache earlier. */
                LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_arp_input: incoming ARP reply\n"));
#if (LWIP_DHCP && DHCP_DOES_ARP_CHECK)
                /* DHCP wants to know about ARP replies from any host with an
                 * IP address also offered to us by the DHCP server. We do not
                 * want to take a duplicate IP address on a single network.
                 * @todo How should we handle redundant (fail-over) interfaces?
                 * */
                dhcp_arp_reply(netif, &sipaddr);
#endif
                break;
        default:
                LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_arp_input: ARP unknown opcode type %"S16_F"\n", htons(hdr->opcode)));
                break;
        }
        /* free ARP packet */
        pbuf_free(p);
}

/**
 * Resolve and fill-in Ethernet address header for outgoing packet.
 *
 * For IP multicast and broadcast, corresponding Ethernet addresses
 * are selected and the packet is transmitted on the link.
 *
 * For unicast addresses, the packet is submitted to etharp_query(). In
 * case the IP address is outside the local network, the IP address of
 * the gateway is used.
 *
 * @param netif The lwIP network interface which the IP packet will be sent on.
 * @param ipaddr The IP address of the packet destination.
 * @param pbuf The pbuf(s) containing the IP packet to be sent.
 *
 * @return
 * - ERR_RTE No route to destination (no gateway to external networks),
 * or the return type of either etharp_query() or netif->linkoutput().
 */
err_t etharp_output(struct netif *netif, struct ip_addr *ipaddr, struct pbuf *q)
{
        struct eth_addr *dest, *srcaddr, mcastaddr;
        struct eth_hdr *ethhdr;
        u8_t i;

        /* make room for Ethernet header - should not fail */
        if (pbuf_header(q, sizeof(struct eth_hdr)) != 0)
        {
                /* bail out */
                LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE | 2, ("etharp_output: could not allocate room for header.\n"));
                LINK_STATS_INC(link.lenerr);
                return ERR_BUF;
        }

        /* assume unresolved Ethernet address */
        dest = NULL;
        /* Determine on destination hardware address. Broadcasts and multicasts
         * are special, other IP addresses are looked up in the ARP table. */

        /* broadcast destination IP address? */
        if (ip_addr_isbroadcast(ipaddr, netif))
        {
                /* broadcast on Ethernet also */
                dest = (struct eth_addr *)&ethbroadcast;
                /* multicast destination IP address? */
        } else if (ip_addr_ismulticast(ipaddr))
        {
                /* Hash IP multicast address to MAC address.*/
                mcastaddr.addr[0] = 0x01;
                mcastaddr.addr[1] = 0x00;
                mcastaddr.addr[2] = 0x5e;
                mcastaddr.addr[3] = ip4_addr2(ipaddr) & 0x7f;
                mcastaddr.addr[4] = ip4_addr3(ipaddr);
                mcastaddr.addr[5] = ip4_addr4(ipaddr);
                /* destination Ethernet address is multicast */
                dest = &mcastaddr;
                /* unicast destination IP address? */
        } else
        {
                /* outside local network? */
                if (!ip_addr_netcmp(ipaddr, &(netif->ip_addr), &(netif->netmask))) {
                        /* interface has default gateway? */
                        if (netif->gw.addr != 0) {
                                /* send to hardware address of default gateway IP address */
                                ipaddr = &(netif->gw);
                                /* no default gateway available */
                        } else {
                                /* no route to destination error (default gateway missing) */
                                return ERR_RTE;
                        }
                }
                /* queue on destination Ethernet address belonging to ipaddr */
                return etharp_query(netif, ipaddr, q);
        }

        /* continuation for multicast/broadcast destinations */
        /* obtain source Ethernet address of the given interface */
        srcaddr = (struct eth_addr *)netif->hwaddr;
        ethhdr = q->payload;
        for (i = 0; i < netif->hwaddr_len; i++)
        {
                ethhdr->dest.addr[i] = dest->addr[i];
                ethhdr->src.addr[i] = srcaddr->addr[i];
        }
        ethhdr->type = htons(ETHTYPE_IP);
        /* send packet directly on the link */
        return netif->linkoutput(netif, q);
}

/**
 * Send an ARP request for the given IP address and/or queue a packet.
 *
 * If the IP address was not yet in the cache, a pending ARP cache entry
 * is added and an ARP request is sent for the given address. The packet
 * is queued on this entry.
 *
 * If the IP address was already pending in the cache, a new ARP request
 * is sent for the given address. The packet is queued on this entry.
 *
 * If the IP address was already stable in the cache, and a packet is
 * given, it is directly sent and no ARP request is sent out.
 *
 * If the IP address was already stable in the cache, and no packet is
 * given, an ARP request is sent out.
 *
 * @param netif The lwIP network interface on which ipaddr
 * must be queried for.
 * @param ipaddr The IP address to be resolved.
 * @param q If non-NULL, a pbuf that must be delivered to the IP address.
 * q is not freed by this function.
 *
 * @return
 * - ERR_BUF Could not make room for Ethernet header.
 * - ERR_MEM Hardware address unknown, and no more ARP entries available
 *   to query for address or queue the packet.
 * - ERR_MEM Could not queue packet due to memory shortage.
 * - ERR_RTE No route to destination (no gateway to external networks).
 * - ERR_ARG Non-unicast address given, those will not appear in ARP cache.
 *
 */
err_t etharp_query(struct netif *netif, struct ip_addr *ipaddr, struct pbuf *q)
{
        struct eth_addr * srcaddr = (struct eth_addr *)netif->hwaddr;
        err_t result = ERR_MEM;
        s8_t i; /* ARP entry index */
        u8_t k; /* Ethernet address octet index */

        /* non-unicast address? */
        if (ip_addr_isbroadcast(ipaddr, netif) ||
                        ip_addr_ismulticast(ipaddr) ||
                        ip_addr_isany(ipaddr))
        {
                LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_query: will not add non-unicast IP address to ARP cache\n"));
                return ERR_ARG;
        }

        /* find entry in ARP cache, ask to create entry if queueing packet */
        i = find_entry(ipaddr, ETHARP_TRY_HARD);

        /* could not find or create entry? */
        if (i < 0)
        {
                LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_query: could not create ARP entry\n"));
                if (q) LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_query: packet dropped\n"));
                return (err_t)i;
        }

        /* mark a fresh entry as pending (we just sent a request) */
        if (arp_table[i].state == ETHARP_STATE_EMPTY)
        {
                arp_table[i].state = ETHARP_STATE_PENDING;
        }

        /* { i is either a STABLE or (new or existing) PENDING entry } */
        LWIP_ASSERT("arp_table[i].state == PENDING or STABLE",
                    ((arp_table[i].state == ETHARP_STATE_PENDING) ||
                     (arp_table[i].state == ETHARP_STATE_STABLE)));

        /* do we have a pending entry? or an implicit query request? */
        if ((arp_table[i].state == ETHARP_STATE_PENDING) || (q == NULL))
        {
                /* try to resolve it; send out ARP request */
                result = etharp_request(netif, ipaddr);
        }

        /* packet given? */
        if (q != NULL)
        {
        	    /* Make sure the up to date entry status is read in. Shouldn't make signeficant performance degrade. */
        		sysFlushCache(D_CACHE);
                /* stable entry? */
                if (arp_table[i].state == ETHARP_STATE_STABLE) {
                        /* we have a valid IP->Ethernet address mapping,
                         * fill in the Ethernet header for the outgoing packet */
                        struct eth_hdr *ethhdr = q->payload;
                        for (k = 0; k < netif->hwaddr_len; k++) {
                                ethhdr->dest.addr[k] = arp_table[i].ethaddr.addr[k];
                                ethhdr->src.addr[k]  = srcaddr->addr[k];
                        }
                        ethhdr->type = htons(ETHTYPE_IP);
                        LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_query: sending packet %x\n", (void *)q));
                        /* send the packet */
                        result = netif->linkoutput(netif, q);
                        /* pending entry? (either just created or already pending */
                } else if (arp_table[i].state == ETHARP_STATE_PENDING) {
#if ARP_QUEUEING /* queue the given q packet */
                        struct pbuf *p;
                        /* copy any PBUF_REF referenced payloads into PBUF_RAM */
                        /* (the caller of lwIP assumes the referenced payload can be
                         * freed after it returns from the lwIP call that brought us here) */
                        p = pbuf_take(q);
                        /* packet could be taken over? */
                        if (p != NULL) {
                                /* queue packet ... */
                                if (arp_table[i].p == NULL) {
                                        /* ... in the empty queue */
                                        pbuf_ref(p);
                                        arp_table[i].p = p;
#if 0 /* multi-packet-queueing disabled, see bug #11400 */
                                } else {
                                        /* ... at tail of non-empty queue */
                                        pbuf_queue(arp_table[i].p, p);
#endif
                                }
                                LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_query: queued packet %x on ARP entry %"S16_F"\n", (void *)q, (s16_t)i));
                                result = ERR_OK;
                        } else {
                                LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_query: could not queue a copy of PBUF_REF packet %x (out of memory)\n", (void *)q));
                                /* { result == ERR_MEM } through initialization */
                        }
#else /* ARP_QUEUEING == 0 */
                        /* q && state == PENDING && ARP_QUEUEING == 0 => result = ERR_MEM */
                        /* { result == ERR_MEM } through initialization */
                        LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_query: Ethernet destination address unknown, queueing disabled, packet %x dropped\n", (void *)q));
#endif
                }
        }
        return result;
}

err_t etharp_request(struct netif *netif, struct ip_addr *ipaddr)
{
        struct pbuf *p;
        struct eth_addr * srcaddr = (struct eth_addr *)netif->hwaddr;
        err_t result = ERR_OK;
        u8_t k; /* ARP entry index */

        /* allocate a pbuf for the outgoing ARP request packet */
        p = pbuf_alloc(PBUF_LINK, sizeof(struct etharp_hdr), PBUF_RAM);
        /* could allocate a pbuf for an ARP request? */
        if (p != NULL)
        {
                struct etharp_hdr *hdr = p->payload;
                LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_request: sending ARP request.\n"));
                hdr->opcode = htons(ARP_REQUEST);
                for (k = 0; k < netif->hwaddr_len; k++) {
                        hdr->shwaddr.addr[k] = srcaddr->addr[k];
                        /* the hardware address is what we ask for, in
                         * a request it is a don't-care value, we use zeroes */
                        hdr->dhwaddr.addr[k] = 0x00;
                }
                hdr->dipaddr = *(struct ip_addr2 *)ipaddr;
                hdr->sipaddr = *(struct ip_addr2 *)&netif->ip_addr;

                hdr->hwtype = htons(HWTYPE_ETHERNET);
                ARPH_HWLEN_SET(hdr, netif->hwaddr_len);

                hdr->proto = htons(ETHTYPE_IP);
                ARPH_PROTOLEN_SET(hdr, sizeof(struct ip_addr));
                for (k = 0; k < netif->hwaddr_len; ++k) {
                        /* broadcast to all network interfaces on the local network */
                        hdr->ethhdr.dest.addr[k] = 0xff;
                        hdr->ethhdr.src.addr[k] = srcaddr->addr[k];
                }
                hdr->ethhdr.type = htons(ETHTYPE_ARP);
               // sysprintf("send arp req\n");
                /* send ARP query */
                result = netif->linkoutput(netif, p);
                /* free ARP query packet */
                pbuf_free(p);
                p = NULL;
                /* could not allocate pbuf for ARP request */
        } else
        {
                result = ERR_MEM;
                LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE | 2, ("etharp_request: could not allocate pbuf for ARP request.\n"));
        }
        return result;
}
